1. Field of the Invention
This invention relates to the storage of data on single-reel cartridges containing a length of magnetic recording tape, and more specifically, to a take-up reel for a single-reel cartridge transport.
2. Related Art
The data processing industry stores large amounts of digital data on magnetic tapes. The 3480 tape cartridge (developed by IBM Corporation, Armonk, N.Y. U.S.A.) is an industry standard for magnetic storage media. The 3480 cartridge includes a single reel with a length of 1/2 inch wide magnetic tape wrapped thereon. Data is stored on the-tape in a longitudinal format.
The cartridge housing protects the tape from damage while allowing the tape reel to be driven from a drive mechanism on the underside of the cartridge housing. The tape is withdrawn from an opening formed at one corner of the cartridge. A leader block attached to a free end of the tape allows the tape to be withdrawn from the cartridge for read/write operations.
Read/write operations are performed by a tape "transport." The standard tape transport accepts the tape cartridge into an elevator assembly. A threading mechanism grabs the leader block and pulls it free from the cartridge. The leader block is then used to thread the tape through a series of guide posts, across a longitudinal read/write head, and into a slot in a take-up reel. Once threaded, the tape from the cartridge can be driven across the read/write heads for data transfer operations.
The leader block and take-up reel are precisely manufactured so that when the leader block is inserted into the slot in the take-up reel, the slot is closed by the end of the leader block so that a relatively smooth surface is created on the hub of the take-up reel for winding the tape on the hub. Ideally, the leader block covers the opening to the slot such that the interface between the top of the leader block and the hub of the take-up reel is perfectly smooth. Unfortunately, however, such a perfectly smooth interface is not practical to manufacture. Therefore, small discontinuities between the leader block and the hub are always present. Such discontinuities can cause impressions in the first wraps of the tape around the hub.
The impressions may affect as many as the first few hundred wraps. The tighter the tape is wrapped, the more pronounced will be the impressions. Moreover, as more wraps are put on the hub, the pressure from the outer wraps accumulates to exacerbate the impressions on the inner wraps.
Tape impressions are highly undesirable. Data bits written on the area of an impression may not be consistently retrievable due to the deformation of the tape media. This results in data errors. Conventionally, to reduce these data errors, the leader block and take-up reel hub have been manufactured to close tolerances in an attempt to reduce the discontinuity between the end of the leader block and the take-up reel hub. Nonetheless, tape impressions still occurred. To insure data integrity, the conventional practice has been to not write data to the portions of the tape having impressions. For example, if the first 100 wraps of the tape were affected by tape impressions, then the practice in the industry has been to not store data on those first 100 wraps of the tape.
Tape impressions are a continuing problem in the data storage industry. Not using the portion of the tape with impressions results in wasted data storage capability and wasted time, as the tape must always be advanced past the unusable portions. What is needed is a means for substantially reducing or eliminating the cause of tape impressions so that the maximum amount of storage capacity can be obtained from each tape cartridge.